The overall goal of this project is to clarify some of the mechanisms that are central to our understanding of endothelial cell (EC) participation in homeostasis. This end point is directly related to the concept that EC are "more than a barrier"...that they contain the primary receptor sites involved in a servo-mechanism between blood and tissues. The experimental procedures will focus on the transport and metabolic responses of EC to vasoactive substances, such as serotonin, catecholamines, prostaglandins and angiotensin, and to platelets and their secretions. The homeostatic importance of these circulating substances as mitogens and as a stimulus for EC calcium mobilization (as a second messenger or in stimulus-coupling) will be investigated. Intrinsic to this research program will be parallel studies to validate that EC cultures are a suitable experimental model for investigating physiological events that are believed to occur in EC in situ and in vivo. Towards this end point the functional characteristics of EC in culture will be studied to determine if: (1) they belong to the cell itself or if they are the result of the in vitro environment; (2) these traits are subsequently effected by subculturing and by storage at -80 degrees C. In addition, we shall continue to investigate the biochemical-physical environment that will optimize the EC functions under investigation. Lastly, an in vivo study utilizing the pulmonary circulation of intact dogs as our model will provide complementary data to our in vitro studies. It is our thesis that the pulmonary EC are intimately involved in the sequelae of events leading to and following respiratory failure and subsequent myocardial depression. Specifically, we wish to define the metabolic consequence of positive end expiratory pressure, and decreased compliance and increased physiologic shunt on the pulmonary EC metabolism of vasoactive materials.